Well, note that in order to be forced to fall back, a massive unit first has to be suppressed and that can only happen if it's been hit by another massive unit. So non-massive units can cause fall back, but only once a massive unit has suppressed the target.
Why did I do this? Like I said: to give conventional units a bit more "oomph" without making them able to push massive units back on their own.
Think of it this way: if the unit has been under heavy fire from another massive unit, it's more sensitive to fire of all sorts as its defensive systems have been overloaded.
It still can't be killed by multiple fallbacks, however.
An example of these rules being used in play can be found here:
http://leadnobleed.blogspot.com.br/2010/06/dave... But let's look at firing for damage...
Dave is a cybertank with six hits, a save of 3 and a damage threshold of three. He charges a company of 3 MBTs who have 4 attack dice each.
The MBTs open up and will hit Dave an average of 8 times. Dave, however, will save about 5 of those.
If the MBTs aren't 'firing to damage', but are just making a normal attack, they don't roll for supression or fallback and those three hits go away at the end of Dave's turn.
If, however, the owner of the MBTs declares he's firing to damage, and scores 3 hits, he'll take a damage point off of Dave, immediately and permanently (they still won't roll for suppression or fallback, however, being non-massive attacks).
If the MBTs score 4 or 5 hits, Dave'll permanently lose a damage point and the extra hits are ignored (they don't carry over to other "fire to damage" attacks, even by the same group of units).
If the MBTs get really lucky and score 6 hits, congratulations! Dave immediately loses 2 hits, permanently (and the MBTs' owner also curses fate because that attack would have killed Dave if it hadn't been declared as "fire to damage"
.
Now, let's say Dave takes two permanent hits from this "fire to damage" attack. The attacker then rolls 2 dice for sixes. He gets a six, meaning he then rolls a critical hit. He rolls a "4".
Dave thus loses one of his secondary weapons. (That should actually be "secondary or tertiary".) The MBTs' owner rolls to see whether Dave loses his secondary battery or his missiles.
Dave's player has a little card or record sheet where all this permanent and critical damage is kept track of.
As Toxic Pixie remarks, this is chrome, but it's hopefully not chrome-plated chrome.
These rules should be used in games with a realtively small number of massive units. They are simple enough, however, that I think you could run a dozen or so massive units per side without these rules really getting in the way. In a big game could always make up some "permanent damage markers" (eschewing the paper work) and simply say that a critical hit means 1D3 more permanent damage.
Hope this helps, SCAdian!